In the graphics arts, it is often desirable to produce a four or more color proof from image data to assist a printer in correcting a set of color prints prior to using the image data to produce color plates and also to reproduce the color quality that will be obtained during the printing process. The proof must be a consistent duplication of the half tone image from a priming process, and should neither gain nor lose color in comparison to the printed image. Visual examination of a color proof should show the following characteristics:
1. defects on the negatives, PA0 2. best color rendition to be expected from press printing of the material, PA0 3. correct gradation of all colors and whether grays are neutral, and PA0 4. need, if any, for subduing one of the colors and/or giving directions for altering the film negatives before making the printing plates. PA0 (a) a flexible support base film; and PA0 (b) a colorant layer comprising a reactive polymeric dye and adjuvants.
Color proofing for multi-colored printing without the use of pre-press color proofs are made by using a printing press or a proof press taking all the steps necessary for actual multicolor printing. Such a conventional method of color proofing is costly and time consuming.
Photographic processes are known that use photopolymers. There are various types of photographic color proofing methods, for example, the surprint type (laminated single sheet) and the overlay type.
Presently, aqueous developable color proofing constructions utilize resin-dispersed pigments. Such resins have to provide a good pigment dispersion but must also be compatible with photooligomers or photopolymers used in the color proofing construction. Unfortunately, dispersed pigments are prone to migration into adjacent layers of the proofing construction, thus contributing to colorant bleeding.
In the overlay type of color proofing method, an independent transparent plastic support is used for producing a print of each color separation film by applying a photosensitive layer of the corresponding color. A plurality of such supports carrying prints of corresponding colors are then superimposed upon each other on a white sheet to produce a color proof. The primary advantage of overlay type of color proofing is that it is quick and can serve as an overlay proof by combining at least three or four colors in register.
In the surprint (adhesively laminated single sheet construction) type of color proofing method, a color proof is prepared by successively producing prints of different colors from different color separation films, respectively, by applying a photosensitive coating of photopolymers of corresponding color on the opaque support in succession. Alternatively, each color separation can be prepared by applying a photosensitive coating of photopolymers of the corresponding color to a strippable support base film and then adhesively laminating the separate color prints together, in register, to prepare a full color proof. Some examples are described in U.S. Pat. Nos. 3,671,236 and 3,136,637. An advantage of this surprint type of color proof is that the color saturation is not influenced by the plastic support. This method more closely resembles the actual printing process and eliminates the color distortion inherent in the overlay system.
An another example of a color-proofing system is one described in U.S. Pat. No. 3,671,236 wherein a light-sensitive continuous color layer is releasably attached to a carrier. Overlaying the color layer is a water-insoluble transparent colorless barrier layer, to the opposite surface of which can be applied a pressure-sensitive adhesive. Upon lamination of the sheet to a substrate, and removal of the carrier, the color layer is formed onto an image, photomechanically, by removal thereof in the non-image areas.
In addition to overlay or surprint types of color proofing, other processes for producing copies of an image embodying a photopolymerization and thermal transfer techniques are known. Some examples are described in U.S. Pat. Nos. 3,060,023, 3,060,024, 3,060,025, 3,481,736, and 3,607,264. Generally, in these processes, a photopolymerizable layer coated on a suitable support is exposed, imagewise to a process transparency. The surface of the exposed layer is then pressed into contact with the image receptive surface of a separate element and at least one of the elements is heated to a temperature above the transfer temperature of the unexposed portions of the layer. The two elements are then separated, whereby the thermally transferable, unexposed image areas of the composition transfer to the image receptive element. If the element is not precolored, the tacky unexposed image may now be selectively colored with a desired toner. The colored matter adheres, preferentially, to the clear unpolymerized material. Since lamination, exposure and development are carried out for the respective colors, in sequence, these processes are generally time consuming.
Typically, the proofing constructions add an oxygen barrier between the support base film and the colorant layer. However, such barriers can fracture along the edges of the transparent sheet, or along the peel front, thus permitting entry of oxygen. The oxygen prohibits photopolymerization. Furthermore, several barriers are susceptible to water damage and render the construction ineffective and non-functional.
U.S. Pat. No. 4,239,868 teaches the preparation and use of structurally colored cross-linkable compositions. These materials are formed by the copolymerization of free-radically polymerizable dyes and acrylates with pendent hydroxy functionality. The hydroxyl groups are subsequently derivatized with an ethylene-containing group, to render the colored polymer cross-linkable. The polymers have relatively low molecular weights, that is, in the range of 1,000-12,800 Daltons.
Examples of other polymeric dyes developed had molecular weight in the range of 4500-5000 and can contained up to 15% dye. For example, an ionomeric macromolecular dye based on polyvinylamine and used in foodstuffs are described in U.S. Pat. Nos. 3,920,855, 3,937,851, 4,275,002 and 4,279,662.